In the master policy ( not likely in your policy booklet from work) is a section that outlines how over payments such as CPP and other lump sum amounts you may receive and be required to reimburse the Insurer is to be paid back.
In my husbands policy he has 6 months to pay back any over payments made on his claim. There was also a recent court decision that allowed a claimant to have the lump sum pro-rated over the policy until he turned 65-pointing out that an Insured may prefer this. That insured had under the over payment provision in his policy the right to opt for that. This maybe another good reason to not sign the irrevocable consent to deduct and pay an Insurer directly form.
No doubt your Insurer will coerce you to pay back your overpayment in full immediately. Do Not Listen To Them -Read Your Master Policy! Although you are required to pay back the benefits, doing so in full places you at risk of having your benefits denied and the insurer keeping your money. At this point, you must subscribe to the Second Golden Rule: “He who has the gold makes the rules.” You will instruct the insurer to take the overpayment from your future benefits. Better for you to budget yourself from funds in savings than to hope for payment each month from a greedy insurer who can deny your claim at will with little recourse to it.
This is just a thought-for many it may not be worth the aggravation.